This application claims the priority benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2005-352881 filed on Dec. 7, 2005, and Japanese Patent Application No. 2005-376132 filed on Dec. 27, 2005 which are hereby incorporated in their entirety by reference.
1. Field
The disclosed subject matter relates to a vehicle light such as a vehicle headlight, a vehicle auxiliary light, spot light, traffic light, and the like, having a diffusion plate for diffusing light. In particular, the disclosed subject matter relates to a vehicle light which can widen the diffusion angle of light that is irradiated in an emitting direction of the vehicle light, thereby improving the light utilization efficiency.
Furthermore, the disclosed subject matter relates to a vehicle light which can widen the diffusion angle of light being irradiated in an emitting direction of the vehicle light, thereby improving the light utilization efficiency in comparison with the case where only light passing through the diffusion plate and being refracted by the diffusion plate is irradiated in the emitting direction.
2. Description of the Related Art
FIG. 1 is a perspective view of a conventional vehicle light 100. Reference numeral 101 denotes a light source such as a filament coil for a light source, or a high light intensity part of a discharge lamp. Reference numeral 102 denotes a bulb containing the light source 101, and reference numeral 103 denotes a socket hole through which the bulb 102 is mounted. Reference numeral 104 denotes a reflector. The surface of the reflector 104 is formed as a single complex reflecting surface extending in the right and left direction. Another type of reflector for a vehicle headlight includes a conventional multi-reflector (not shown) having a plurality of reflecting surfaces. Before developing such a multi-reflector for a vehicle headlight, a revolved parabolic surface had been mainly adopted as the reflecting surface of a vehicle headlight.
In FIG. 1, reference numeral 105 denotes a cover lens or a front lens, and reference numeral 106 denotes a grouped lens composed of lens cuts arranged on the center part of the cover lens 105. The conventional vehicle light 100 as shown in FIG. 1 has a number of convex lens portions side by side serving as the grouped lens.
In the conventional vehicle light 100 shown in FIG. 1, light diffused in the right to left direction can be irradiated in front of the vehicle light 100. However, a light loss of typically 10 to 20% has occurred due to the provision of the grouped lens 106 that has lens cuts. In more detail, part of light incident on the lens cuts 106 is reflected by the incident surface of the lens cut 106 (surface on the light source 101 side) and the emitting surface (surface on the front side of the vehicle light 100), thereby returning the light back to the light source 101 side.
Furthermore, the conventional vehicle light 100 as shown in FIG. 1 has an acute lens cut in order to irradiate diffusion light with an angle of 30° or more with respect to the main optical axis of the light 100. In other words, it is necessary to increase the incident angle of light incident on the incident surface and the emitting surface of the grouped lens or lens cut 106. In this case, the ratio of reflected light returned back to the light source 101 side from the incident and emitting surfaces may increase. As a result, the ratio of light irradiated in the irradiation direction of the vehicle light 100 may decrease. Therefore, the light is attenuated and the diffused light with an angle of 30° or more with respect to the main optical axis of the light 100 may not increase, resulting in a darker vehicle light.
FIG. 2 shows an example of a lens cut which provides an adverse affect when an incident angle is made larger. In this lens cut of FIG. 2, the difference between the convex and concave portions is large. In this case, the incident angle of light incident on the incident surface and the emitting surface of the lens cut becomes larger. Accordingly, when passing through the incident surface and the emitting surface, the ratio of the reflected light may significantly increase with respect to the refracted light. In case of an extremely large incident angle, the light may be totally reflected. Namely, even when the vehicle light is designed to irradiate diffused light with an angular range of 40° to 50° with respect to the main optical axis of light (vertical direction in FIG. 2), the light irradiated in the irradiation direction of the vehicle light (lower side in FIG. 2) is not diffused and widespread, but is only attenuated. The refraction phenomenon in FIG. 2 can be described in accordance with Snell's law (sin γ/sin i=1/n). In FIG. 2, symbol i and I′ each denote an incident angle (=reflection angle), and symbol γ is a refraction angle. nair (=1) is a refraction index of air and n (≈1.6) is a refraction index of a material forming the lens cut.
Conventionally, vehicle lights with a diffusion plate used for diffusing light have been known. Examples of the diffusion plate include an auxiliary lens for diffusion, an inner lens, a transparent plate, and the like. More specifically, examples of this type of vehicle light includes those shown in FIGS. 4 and 7 of Japanese Patent Laid-Open Publication No. 2003-281906 (hereinafter referred to as a “Publication 1”), that shown in FIG. 4 of Japanese Patent Laid-Open Publication No. 2000-133011 (hereinafter referred to as a “Publication 2”), that shown in FIG. 1 of Japanese Patent Laid-Open Publication No. Hei 9-219105 (hereinafter referred to as a “Publication 3”), and the like, all of which are incorporated herein in their entirety by reference.
The vehicle light shown in Publication 1 may be configured such that the parabolic reflecting surface reflects light and the reflected light passes through an auxiliary lens for diffusion. Furthermore, the light which has passed through the diffusion auxiliary lens is refracted by the diffusion auxiliary lens to be horizontally diffused and irradiated in the irradiation direction of the vehicle light.
This reduces the light utilization efficiency. In addition to this, when the refracted light passing through the diffusion auxiliary lens is largely diffused, the refracted light may only be attenuated without large diffusion. Accordingly, it is difficult to sufficiently diffuse the light with large angles in the irradiation direction using the vehicle light in accordance with the technique of Publication 1.
The vehicle light disclosed in Publication 2 is configured so that the light from a light source is reflected by a reflector and the reflected light is allowed to pass through an inner lens. In this case, the reflected light by the incident surface (surface on the reflector side) and the emitting surface (surface on the front side of the vehicle light) of the inner lens is returned back to the reflector side, without utilizing the light in the irradiation direction. Namely, in the vehicle light disclosed in Publication 2, because the light reflected by the incident surface and the emitting surface of the inner lens are not irradiated in the irradiation direction, the light utilization efficiency may be reduced. In addition to this, when the refracted light passing through the inner lens is largely diffused, the refracted light may only be attenuated without large diffusion. Accordingly, it is difficult to sufficiently diffuse the light with large angles in the irradiation direction using the vehicle light in accordance with the technique of Publication 2.
The vehicle light disclosed in Publication 3 is configured so that the light from a light source is reflected by a parabolic reflector and the reflected light is allowed to pass through a transparent plate. In this case, the light that passes through the transparent plate is refracted by a condensing lens element of the transparent plate to be diffused.
Namely, in the vehicle light disclosed in Publication 3, the refracted light passing through the transparent plate is diffused by the condensing lens element of the transparent plate to be irradiated in the irradiation direction of the vehicle light. In this case, the light reflected by the incident surface (surface on the parabolic reflector side) and the emitting surface (surface on the front side of the vehicle light) of the transparent plate is returned back to the parabolic reflector side, without utilizing the light in the irradiation direction. Namely, in the vehicle light disclosed in Publication 3, the light reflected by the incident surface and the emitting surface of the transparent plate are not irradiated in the irradiation direction. This reduces the light utilization efficiency. In addition to this, when the refracted light passing through the transparent plate is largely diffused, the refracted light may only be attenuated without large diffusion. Accordingly, it is difficult to sufficiently diffuse the light with large angles in the irradiation direction using the vehicle light in accordance with the technique of Publication 3.